The present disclosure relates to energetic compositions, more specifically to bonding agents for hydrazinium nitroformate (HNF) compositions.
Energetic compositions, for example composite solid rocket propellants and composite propellants, include solid particles dispersed in a rubbery matrix, called a binder. A compound that provides oxidizing chemical species to the combustion process and/or liberates energy upon decomposition is a common type of particle used in solid propellant compositions. The structural properties of the energetic composition are influenced by the strength of the bond between the binder and the surfaces of the solid particles. Since the oxidizers can make up a majority of the particulate matter, the bond between the binder and the oxidizer particle surfaces has a significant effect on composition's structural properties.
Ammonium perchlorate (AP) is a common oxidizer used in energetic compositions and chemically reacts with many types of compounds. A number of effective bonding agents exist for energetic compositions in which AP is the principal oxidizer. However, effective bonding agents for energetic compositions in which nitrogen-containing oxidizers, which are less reactive, are the principal solid oxidizer are unknown. Two common nitrogen-containing oxidizers used in energetic compositions are cyclotetramethylenetetranitramine (HMX) and cyclotrimethylenetrinitramine (RDX).
Generally, an effective bonding agent will coat the oxidizer surface, react to form an encapsulating film around the particles, and bond to the binder either chemically or adhesively. If the bonding agent film has sufficient affinity for the oxidizer surface, it will prevent binder/oxidizer separation under stress. The bonding agent may be coated onto the oxidizer particles either before incorporation of the oxidizer into the composition mix or, in some cases, during the composition mixing operation.
The structural properties of energetic compositions derive from a complex interaction of binder properties with the solid oxidizer particles. Further, the composition properties are strongly influenced by particle size and volumetric loading, as well as by the binder/solids bond strength. When the elastomeric binder is strong relative to the binder/solids bond strength, an energetic composition under sufficient tension will undergo separation of the binder from the solids. The separation is sometimes referred to as de-wetting or blanching and is followed by large extensions of the binder prior to rupture. Structurally, such an energetic composition is characterized by high extensibility and low tensile strength. However, when the binder/solids bond strength is increased, as by a bonding agent, de-wetting is prevented or forestalled, resulting in less extensibility and higher tensile strength.
Although effective bonding agents are known, AP poses environmental hazards. In particular, chlorine species are released in exhaust fumes, contaminating the surrounding air and groundwater.
HNF is a salt of the hydrazinium ion (N2H5+) and nitroformate anion (C(NO2)3−). HNF has the potential to serve as an improved, eco-friendly, oxidant in propellants. HNF produces energetic compositions which burn very rapidly and with very high combustion efficiency. Further, HNF's high energy leads to high specific impulse propellants. However, HNF suffers from poor handling sensitivity and incompatibility with known conventional binder systems.